Telephone system.



PATENTED AUG. 8, 1905.

W. W. DEAN. TELEPHONE SYSTEM. APPLICATION FILED 001. 27, 1902.

ANDREW. a. cnmm co.. mom-Lm-loonnnzns, WASHMGTON. I:v r:v

UNITED sTA'gns PATENT OFFICE.

.WILLIAM W. DEAN, OF CHICAGO, ILLINOIS, ASSIGNOR TO KELLOGG SWITCHBOARDAND SUPPLY COMPANY, OF CHICAGO, ILLINOIS, A

CORPORATION OF ILLINOIS.

TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Aug. 8, 1905.

AppIication filed October 27,1902. Serial No. 128,882.

T to whom it may concern.-

Be it known thatLWIL'LIAM WV. DEAN, a citizen of the United States,residing at Chicago, in the county of Cook and State of Illinois, haveinvented new and useful Improvements in Telephone Systems, of which thefollowing is a specification.

My invention relates to telephone systems, and particularly to those ofthe four-division type. In this type of telephone systems it is now wellunderstood the subscribers lines are provided with a calling-signal andan answering-jack upon each division of the switchboard, together withsuitable calling apparatus at the subscribers station for selectivelyactuating any of the said signals. Upon one of the divisions of theswitchboard each line is provided also with a plurality of multiplejacks.

The system of my invention includes common batteries or other commonsources of current at the central oflice for the actuation of allsignals and apparatus, so that the subscribers stations are equippedonly with the necessary mechanical and electrical devices for suitablycompleting the circuits of said central sources.

Although the lines of my invention are provided with a calling-signalupon each of the four divisions of the switchboard, only four relays arerequired for each line, one of said relays being a cut-off relay, whichis actuated when a connection is established with a line at any of itsconnection terminals or springjacks to render the line-signalsinoperative. This cut-off relay serves the further function of placingthe line in condition for conversation by connecting the normallydisconnected jacks or connection terminals with the externalline-circuit.

My invention is illustrated in the accompanying drawing, in which thesame reference characters are used to designate like parts, and in whichthe figure is a diagram of a system, showing two subscribers lines andthe central-office apparatus at one division of the switchboard.

Two subscribers lines L and L are shown extending from their respectivesubstations E and E to the central oiiice. The apparatus at thesubstations is the same throughout the system, so that only that, say,at station E will be specifically described.

This apparatus includes an ordinary polarized signaling-bell 2 and acondenser 3, permanently connected between the line conductors of thetelephoneline and a transmitter 4, and receiver 5 in a normally openbridge of the said conductors, but which is adapted to be closed by theswitch-hook 6 during conversation. A set of calling-keys is alsoprovided for each substation, the key a being adapted to ground the tipline conductor 7 when actuated, the key 6 to ground the sleeve lineconductor 8, the

key 0 to directly ground both conductors 7- and 8, and the key (Z toground both conductors, but with a resistance 9 between the sleeveconductor and the ground branch. These keys at the substation areadapted to operate the line-signals located upon the correspondingdivisions A, B, C, and D of the switchboard. The line is also providedwith an answering-jack J upon each of the divisions and with multiplejacks upon one of the divisions. The multiple jacks for the line L areshown at J and J upon division C. Pilotsignals S common to all of thelines upon each operators position, are provided for each of thedivisions, the circuits of these pilotsignals being controlled by thepilot-relays R. Three line-relays R, R and R* are provided for eachline, and a cut-off relay R is also furnished for the line. ductor 7terminates in the spring 10 of the cut-off relay R", the normal contact11 of which is connected, by means of conductor 12, with onedifferential winding 13 of the linerelay R the opposite terminal ofwhich is connected by conductor 14 with actuatingwinding 15 of theline-relayR and thence by conductor 16 with the battery-lead 17,extending to the live pole of the battery F, the opposite pole of whichis grounded. The other line conductor 8 is connected with the spring 18of the cut-off relay R the normal contact 19 of which is connected byconductor 20 with the other differential winding 21 of line-relayR andthence by conductor 22 with the actuating-winding 23 of line-relay R andthence over branch 25 to the batterylead 17. The forward contact 26 ofspring 10 of the cut-off relay is joined by conductors 27 and 28 withthe tip-springs of all of the jacks or connection terminals of the line,while the forward contact 29 of spring 18 of thecut-off relay iselectrically connected The tip line con with the locking-winding of theline-relay R. branch conductor 36 extends from said conductor 34 to thelocking-winding 37 of line-relay R and a similar branch 38 leads tolocking-winding 39 of relay R The locking-winding of line-relay R hasits circuit completed through the normal contact and spring 40 of saidrelay and conductor 41 to the battery-lead 17, while line-relay R hasthe circuit of itslocking-winding completed through the forward contactand spring 42 and conductor 43 to the said battery-lead 17, and thecircuit of the locking-winding of relay R is likewise completed throughthe for- I ward contact 44 and spring 45 and conductor 46 to the saidbattery-lead. The circuit of the signal-lamp S in division A oftheswitchboard is completed from ground by conduc tor 47,which includes thepilot-relay R, thence by conductor 48, spring 49, and forward contactofline-relay R", conductor 50, spring 51, and forward contact of relay Rconductor 52, normal contact, and spring 45 of relay 11*, and thence byconductor 46 to the batterylead 17. The corresponding lamp in division Bhas its circuit completed from ground by conductor 53, including thepilot-relay R, conductor 54, spring 55, and normal contact of relay R,conductor 56, spring 57, and forward contact of relay R conductor 58,the forward contact and spring 45 of relay R and conductor 46 to thebattery-lead 17. The lamp in division C has its circuit completed fromthe battery-lead 17 by means of conductor 59, including the pilot-relayR, the lamp,

conductor 60, spring 61, and forward contact of relay 3*, conductor 62,normal contact, and spring 63 of line-relay R conductor 64, forwardcontact and spring 65 of relay R, and thence to ground. The lamp indivision D has its circuit likewise completed from the battery-lead 17by means of conductor 66, in-

cluding the winding of the pilot-relay R, the lamp, conductor 67, spring68, and forward contact of line-relay R", conductor 69, forward contact,and spring 63 of line-relay R conductor 64, forward contact, and spring65 of relay R and thence to ground. The pilotsignals in each of thesedivisions, preferably in the form of small incandescent lamps, are fedfrom the battery-lead 17, as shown.

The central-ofiice apparatus at the division D is intended to be shownby the diagram of l the cord-circuit and associated apparatus. It willbe understood that all of the divisions and all of the operatorspositions are provided The I with a plurality of said cord-circuits andap* paratus. The cord-circuit shown comprises 1 the answering-plugP andthe calling-plug P having tip and sleeve contact-surfaces adapted toregister with the like surfaces in the jacks of the lines. Thetip-contacts of the two plugs are connected together by the strands tand t with an interposed condenser 0 while the sleeves of the plugs arejoined by the strands s and s and the condenser 0 The battery F isbridged across between the strands t and s and includes upon either sidethe supervisory relays a" and W, which control the local circuit of thesupervisory signal S associated with the answering-plug, the relayserving to normally close said local circuit the relay 1' to normallyopen the same. The battery F is bridged across the calling end of thecord-circuit and includes upon either side the similar supervisoryrelays r and 7 controlling the former through its normally closedcontacts and the latter to its normally open contacts the local circuitof the supervisory signal S*, associated with the callingplug. Thetip-strand t of the called circuit is normally open at spring ofsupervisory relay R, the normal contact of which is joined by conductor71 with the high-resistance and high-impedance test-relay r", theopposite terminal of which is grounded through conductor 72. The forwardcontact of said spring 70 is connected with the remainder of the tipstrand, whereby when said supervisory relay is actuated the test-relayis cut off and the ti p-strand of the cord-circuit is completed forconversation. The operators receiver 73, the secondary of her induction74, and the'condenser 0 are adapted to be connected in a bridge of thecord-circuit by the springs 75 of the listening-key. Her transmitter 76is i connected on one side to ground by conductor 72 and on the otherside by conductors 77 and 78 with the battery-lead 17, extending fromthe live pole of the battery F, the conductor 78 including animpedance-coil 79. The primary of herinduction-coil 74 together with thecondenser are connected in shunt of the transmitter 76. The spring 80 ofthe test-relay r is grounded and the forward'contact of said spring isconnected with the shunt containing the primary of the op eratorsinduction-coil. A ringing-generator 81 is adapted to be connectedtogether with a resistance-lamp 82 between ground and the tipspring ofthe ringing-key 83 83 of the cordcircuit, while the sleeve -spring ofsaid key when actuated connects with said battery- I lead 17 andincludes the resistance 84.

The operation is as follows: By pressingthe key a at the substation thesignal in the A division of the switchboard is actuated over the overthe tip line conductor- 7, contacts 10 and 11 of the cut-off relay B",conductor 12, winding 13 of the difierential line-relay R conandfollowing path: from ground at said key ductor 14, winding 15 of relay Rconductor 16, and the battery-lead 17 to the live pole of battery F, andthence to ground. The completion of this path actuates both relays R andR the circuit of the locking-winding of relay R being completed from thebatterylead 17 over conductor 41, spring 40, and front contact of relayR locking-winding 39, conductors 38 and 34, normal contact and spring 33of cut-off relay R to ground, while the circuit for the locking-windingof relay R is completed from the battery-lead 17, conductor 43,spring42, its forward contact, winding 37 of relay R conductors 36 and 34, andspring 33 to ground. These relays are therefore locked in actuatedcondition, even though the calling-keya be released. The actuation ofthese two relays efiects the closing of the circuit of the signal-lampS, said circuit being traced from ground at said signal, the pilotrelayR, signal S, conductor 48, spring 49 of relay R its forward contact,theconductor 50, spring 51 of relay R its forward contact, conductor 52,and the normal contact of spring 45 of relay R, which is not actuated,and thence by conductor-46 and battery-lead 17 to the battery F. Thislamp is therefore lighted and the pilot-relay is energized to close thecircuit of the pilot-lamp S from the batterylead 17. It will be noticedthat the actuation of the relay R opens the circuit of the signal-lampin the B division of the switchboard through its spring 55, that thecircuit of the lamp in the C division of the switchboard is open atspring 61 of relay Rfland that the lampcircuit of the D division is openat spring 68 of the relay R", for which reasons only the lamp Aoperates.

In case it be desired to operate the signal upon the B division of theswitchboard the key 6 is actuated at the substation and a path forcurrent is completed over a circuit similar to that before described forthe key a, except that the relays R and R are now operated and the relayR does not respond. This results in closing an actuating-circuit for thesignal-lamp upon the B division from ground at said signal through thepilotrelay R, lamp S, conductor 54, spring 55 of relay R and its normalcontact, conductor 56, spring 57, and the forward contact of thelinerelay R conductor 58, the forward contact, and spring 45 of relay R,and thence by con ductor 46 to battery-lead 17. The lockingcircuits arecompleted, as before described, through the ground spring 33 of thecut-off relay, whereby when a connection is established in response tothe signal, as hereinafter described, and the cut-off relay R isactuated the said locking-circuits are opened at said spring 33. Thecircuit of the lamp upon the A division is now open at spring 45 ofrelay R. The circuit of the lamp upon the 0 division is open at spring63 of relay R while the similar lamp upon the D division remains open atspring 65 of relay R The lamp at the C division of the switchboard maybe selectively operated from the substation by key 0, which serves toground both conductors 7 and 8 of the line-circuit, thus permittingcurrent to flow from the live pole of the battery F over the two pathssingly traced for the keys 0/ and b, but with the result that the equalcurrents flowing through the differential windings of the relay R areneutralized, thus preventing the operation of said relay, while the tworelays r and 0'' respond to these currents and are therefore actuatedand locked up. The operation of these two relays effects the closing ofthe signallamp at the O division from the battery-lead 17 over conductor59, through the pilot-relay R, the signal-lamp S, conductor 60, spring61 of relay Rfl its forward contact, conductor 62, the normal contactand spring 63 of relay R conductor 64, the forward contact and spring 65of relay R to ground. This signal as well as its pilot-signal aretherefore actuated to indicate the call of the subscriberf Although therelays R and R are now operated, the

fact that the springs of relay R are in normal position serves to openthe circuits of the other three lamps of the line, which are thereforeinert. Assuming, however, that the subscriber wishes a connection withanother subscriber having his multiple jacks upon the ID division of theswitchboard, he operates the key (Z with the result, as just described,that both line-wires are grounded, but the conductor 8 has its circuitto ground completed through the five-hundred-ohm resistance-coil 9. Thisresults in unbalancing the magnetic effects of the currents flowingthrough the two differential windings of the relay R which is thusactuated in addition to the other two relays R and R". The simultaneousoperation of these three relays results in closing only one of thesignal-circ uits-namely, that of the lamp located upon the division D,which is completed from the battery-lead 17 over conductor 66, throughthe lamp, conductor 67, spring 68 of relay R and its forward contact,conductor 69, forward contact and spring 63 of relay R, conductor 64,forward contact and spring 65 of relay R to ground. The circuit of theA- division lamp is now open at spring 45 of relay R that of the B lampis open at spring 55 of relay R while the circuit of the Clamp is openat spring 65 of relay R The lighting of this signal is answered by theinsertion of the answering-plug of the operators cordcircuit, whichcompletes a path for current from the live pole of the battery F,through the sleeve supervisory relay r sleeve-strand s of thecord-circuit, sleeve conductors 31 and 30 of the jacks, and through thecut-off relay R to ground. The actuation of this cut-off relay serves todisconnect the line conductors 7 and 8 from the three line-relays and toconnect them with the conductors 27 and 30, leading to the jacks. At thesame time the spring 33 serves to open the circuits of thelockingwindings of said line-relays. which are therefore deenergized andreturn to normal position. The signal-lamps are thus rendered inert andprevented from again operating during the connection. The subscriberhaving taken up his receiver, a complete path over the metallic line isprovided for current from the battery F, whereby both supervisory relaysr and r are operated, the former serving to open the local circuit ofthe supervisory signal S which therefore remains dark. In order toconverse with the subscriber, the operator actuates her listening-key,thus bridging her instrument across the cord-circuit, and upon receivingthe order tests the condition of the wanted line by means of the tip ofthe calling-plug. Under normal conditions the test rings or sleeves ofthe lines are disconnected from any current source; but upon theconnection of the cord-circuit, as just described with reference to theanswering-plug P, the live pole of a battery is connected with thesleeve conductors of the jacks. It therefore follows that thesleeve-rings of all jacks of the line are raised to a potential abovethat of the earth and are in condition to test busy upon the completionof a path for current therefrom to ground or to the other pole of thebattery. Touching the tip of the callingplug completes such atesting-path from the tip of said plug over strand 25 spring 70 ofsleeve supervisory relay r, its normal contact, conductor 71, throughtest-relay 1' and conductor 72 to ground. If the line is idle, thetest-relay will not respond and no click will be received by theoperator; but if the line is busy the test-relay will respond and close,through its armature and forward contact, a path for current from thebattery-lead 17, through impedance-coil 79, and the primary of theinductance-coil to ground. This causes a click in the operatorsreceiver. The high resistance of the test-relay prevents a largevariation of current upon the tested line in case it is connected forconversation, and the high impedance prevents a sudden variation. Uponfinding the line idle the calling-plug P is inserted in one of themultiple jacks of the wanted-subscribers line, and the calling-key 83 83is operated. The insertion of the plug P completes a path over thesleeve-strand of the cord-circuit from the live pole of the battery Fthrough the cut-ofi relay R for the line, which is thus actuated torender all of the line-signals for the line inert. The operation of theringing-keydoes not destroy this condition, for the reason that thesleeve-spring 83 completes a path for current over said battery throughthe resistance-coil 8A and the battery-lead 17, so that the cut-offrelay remains actuated during ringing. Ringing-eurrentis sent out overthe tip side of the line from the generator 81 to the substation andback over the sleeve side of the line and through the said resistance84, the battery-lead 17, and battery F to ground. As soon as theringing-key is released the supervisory relay rof the cordcircuit isactuated to disconnect the test-relay and complete the tip-strand of thecord-circuit for conversation. At the same time the local circuit of thesupervisory signal 8* is closed, and since the tip-relay r is not yetactuated said signal is lighted to indicate the fact of the non-responseof the subscriber. Upon the response of the called subscriber a completepath for current from the battery F is established over the metallicline and over both sides of the cord-circuit,whereby said tipsupervisory relay r responds, thus opening the circuit of thesupervisory signal S and rendering the same inert. The operator is thusapprised of the fact that the subscribers are in communication. At thistime the batteries F and F are furnishing current for the operation ofthe several relays associated with the connected lines and thetransmitters at the substation. At the termination of the conversationthe subscribers return their receivers to the hooks, with the resultthat the metallic lines are opened at the substation and the tipsupervisory relays r and r are deenergized to close the local circuitsof the corresponding supervisory relays S and 8*, which are thuslighted. Upon observing these signals the operator takes down theconnection and all parts are restored to normal position.

The substation apparatus is intended to indicate any desired commonbattery set, and the ringing and listening keys are onlydiagrammatically shown and are intended to designate any ordinary key,preferably the kind in which the actuation of a single lever in onedirection will simultaneously actuate both the tip and sleeve springs.The several grounds referred to may be and in practice usually are oneand the same or the common office-ground or common return. Several setsof batteries may be employed, although it is preferable to use a singleset for the exchange.

Various other modifications may be made in my invention withoutdeparting from the scope or principle of the same.

I claim 7 1. In a telephone system, the combination with atelephone-line, of a relay at the central oflice in each line conductorand actuated thereover, a differential relay having a winding in eachline conductor, and telephonic apparatus affected by said relays whenoperated, substantially as described.

2. In a telephone system, the combination with a telephone-line, of arelay at the central office in each line conductor and actuatedthereover, a differential relay having a Winding in each line conductor,a locking-circuit for each of said relays to maintain the same actuated,and telephonic apparatus affected by said relays when operated,substantially as described.

3. In a telephone system, the combination with a telephone-line having asignal upon each of the four divisions of a switchboard, of three linerelays for the line controlling through their contacts the circuitsofsaid signals; one of said relays having its actuatingwinding in oneconductor, another having its winding in the other line conductor, andthe other relay having a winding in each line conductor differentiallydisposed with reference to current over the two sides of the line inparallel; a central source of current having its live pole connectedwith both of said line conductors, four switches located at thesubstation and corresponding to the four linesignals, two of saidswitches being adapted to ground their respective line conductors tosimultaneously actuate the differential relay,

and the corresponding relay, another of said switches being adapted toground both line conductors whereby the differential relay remainsneutral while the other two are actuated, and the fourth key serving toground both line conductors but includinga resistance in one of saidconductors, whereby the magnetic effects of the current in the two coilsof the differential relay are unbalanced and all relays are actuated,substantially as described.

4. In a telephone system, the combination With a telephone-line, ofnormally disconnected jacks therefor located upon the several divisionsof a divided central switchboard, a signal for the line in each of thedivisions, a plurality of relays for the line less than the number ofsignals, a central common source of current to operate said relays, saidrelays serving to control the circuits of the signals, a cutoffrelay forthe line actuated over a portion of the talking-circuit when aconnection is established with the line at any of the divisions, saidcut-off relay serving when actuated to disconnect said relays andsignals from the line and to connect the spring-jacks therewith,substantially as described.

5. In a divided central system, the combination with a telephone-line,of a plurality of signals therefor located upon the different divisionsof a switchboard, a plurality of relays controlled from the substationto cause the desired operation of said signals, one of said relays beingoperated by current over one line conductor, another by current over theother line conductor, and still another by current over both conductorsof the telephone-line, a central common source of current to furnishcurrent for the operation of said relays, and means to render saidsignals inoperative when a connection is established with the line forconversation at any of the divisions of the switchboard, substantiallyas described.

6. In a divided central system, the combination with a telephone-line,of a plurality of signals therefor located upon the different divisionsof the switchboard, a plurality of relays controlled from the substationto cause the desired operation of said signals, a common source ofcurrent connected with the line at the central office, one of saidrelays being operated by current from said source over one lineconductor, another by current from said source over'the other lineconductor, and still another by current from said source over both lineconductors, and means to render said signals inoperative when aconnection is established with the line for conversation at any of thedivisions of the switchboard, substantially as described.

7. In a divided central system, the combination with a telephone-line,of a plurality of signals therefor located upon the different divisionsof the switchboard, a plurality of relays associated with the line andcontrolled from a substation to cause the desired operation of saidsignals, a common source of cur rent connected with the line at thecentral of- (ice, one of said relays being operated by current from saidsource over both sides of the telephone-line in parallel, and means torender said signals inoperative when a connection is established withthe line for conversation at any of the divisions of the switchboard,substantially as described.

8. In a divided central system, the combination with a telephone-line,of a plurality of signals therefor located upon the different divisionsof the switchboard, a plurality of relays controlled from the substationto cause the desired operation of said signals, a common source ofcurrent connected with the line at the central oflice, one of saidrelays being operated by current from said source over one lineconductor, a second from said source over the other line conductor and athird from said source over'both line conductors in parallel, and meansto render said signals inoperative when connection is established withthe line for conversation at any of the divisions of the switchboard,substantially as described.

9. In a divided central system, the combination with a telephone-line,of a plurality of signals therefor located upon the difierent divisionsof the switchboard, a plurality of relays associated with the line andcontrolled from the substation to cause the desired operation of saidsignals, a common source of current to which the line is connected atthe central ofiice, one of said relays being differential and operatedby current from said source over both sides of the telephone-line,andmeans to render said signals inoperative when a connection isestablished with the line for conversation at any of the divisions ofthe switchboard, substantially as described.

10. In a divided central system, the combination with a telephone-line,of a plurality of signals therefor located upon the different divisionsof the switchboard, a plurality of relays at the central officeassociated with the line and controlled from the substation to cause thedesired operation of said signals, one of said relays being placed ineach line conductor and actuated thereover, and a differential relayhavingawindingin each line conductor, and means to render the saidsignals inoperative when a connection is established with the line forconversation at any of the divisions of the switchboard, substantiallyas described.

11. In a divided central system, the combination with a metallictelephone-line, of a plurality of signals therefor located upon the different divisions of the switchboard, a plurality of relays for the linecontrolled from the substation to selectively cause the operation ofsaid signals, one of said relays having a winding in each side of theline whereby it may be operated by current over either line conductor,and means to render said signals inoperative during connections forconversation with the line at any division of the switchboard,substantially as described.

12. In a divided central system, the combination witha metallictelephone-line, of a plurality of signals therefor located upon thedifferent divisions of the switchboard, a plurality of relays for theline controlled from the substation to selectively cause the operationof said signals, one of said relays being in one line conductor and asecond relay having a winding in each conductor, whereby both re.

lays may be simultaneously operated by current over one side of the lineand the second relay may be operated independently of said first relayby current over the other side of the line, and means to render saidsignals inoperative during connections for conversation with the line atany division of the switchboard, substantially as described.

13. In a divided central system, the combination with a metallictelephone-line, of a plurality of signals therefor located upon thedifferent divisions of the switchboard, a plurality of relays for theline controlled from the substation to selectively cause the operationof said signals, one of said relays being located in each line conductorand a third relay having a winding in each line conductor, whereby saidthird relay may be operated simultaneously with either of the otherrelays by current over the corresponding conductor of thetelephone-line, and means to render said signals inoperative duringconnections for conversation with the line at any division of theswitchboard, substantially as described.

14. In a divided central system, the combination with a metallictelephone-line, of a plurality of signals therefor located upon thedifferent divisions of the switchboard, a plural-- ity of relays for theline controlled from the substation to selectively cause the operationof said signals, one of said relays having a winding in each side of theline and being differential to current over both sides of the line inparallel, and means to render said signals inoperative duringconnections for conversa-' tion with the line at any division of theswitchboard, substantially as described.

15. In a telephone system, the combination with a telephone-line, oftelephonic apparatus associated with the line, three relays adapted tobe operated in different groups to suitably control said apparatus, oneof said relays having a winding in each side of the line differentiallydisposed with reference to current over both sides of the line inparallel whereby the said relay may be operated by current over eitherline conductor and remain inoperative by current over both sides of theline in parallel, substantially as described.

16. In a divided central system, the combination with a metallictelephone-line, of a plurality of signals therefor located upon thedifferent divisions of the switchboard, a plurality of relays for theline controlled from the substation to selectively cause the operationof said signals, one of said relays being in each line conductor and athird havinga winding in each line conductor and being differential tocurrents over the two sides of the line in parallel whereby said thirdrelay and one of the other relays may be operated together by currentover the appropriate line conductor and said first two relays may beoperated together without operating said third relay by current over thetwo sides of the line in parallel, and means to render said signalsinoperative during connections for conversation with the line at anydivision of the switchboard, substantially as described.

17 In a telephone system, the combination with a telephone-line, oftelephonic apparatus associated with the line, three relays for theline, one of said relays being placed in each line conductor, and theother relay having a winding in each side of the line differentiallydisposed with reference to current over the line conductors in parallel,means to cause current flowing over both sides of the line in parallelto produce equal and opposite effects in the differential windings ofsaid relay and unequal effects in said relays, wherebysaid differentialrelay may be operated simultaneously with said other relays or saidother relays may be operated simultaneously without operating saiddifferential relays to affect said telephonic apparatus, substantiallyas described.

18. In a telephone system, the combination with a telephone-line, oftelephonic apparatus associated with the line, three relays for theline, one of said relays being placed in each line conductor and theother relay having a winding in each'line conductor differentiallydisposed with reference to current over both sides of the lines, meansto cause current to flow over either line conductor alone to therebyoperate the corresponding relay and the differential relay, means tocause current to flow over the telephone-line to produce equal andopposite effects in the diflerential relay whereby the other two relaysmay be simultaneously operated Without operating the differential relay,and means to cause current over both sides of the line to produceunequal effects in said difierential coils whereby all of the relays maybe simultaneously operated to affect said telephonic apparatus,substantially as described.

19. In a divided central telephone system, the combination with ametallic telephone-line, of four signals therefor located upon diflerentdivisions of the switchboard, three relays for the line at the centraloffice, one in each line conductor and the third relay having a windingin each side of the line differentially disposed with reference tocurrentover the two sides of the line in parallel, switches at thesubstation for grounding either of the line conductors singly, fordirectly grounding both line conductors simultaneously, and forgrounding both line conductors simultaneously and at the same timeincluding a suitable resistance in the path of current over onelineconductor, a common source of current at the central oifice connectedbetween ground and the two sides of the telephone-line, the cir cuits ofsaid signals being suitably controlled through the contacts of saidrelays whereby the subscriber may cause the simultaneous operation ofthe differential relay, and either of the other relays by current overthe proper line conductor, the simultaneous operation of the twofirst-mentioned relays without operating the differential relay bycurrent over both line conductors and the simultaneous operation of allthree relays by current over both line conductors and through saidresistance tothereby cause the desired operation of any of said signals,substantially as described.

Signed by me at Chicago, county of Cook, State of Illinois,this 23d dayof October, 1902.

WILLIAM W. DEAN.

Witnesses:

ROBERT LEWIS AMES, GAZELLE BEDER.

